Trehalose is a non-reducing disaccharide formed by an α,α-1,1-glucoside bond formed by an α,α-1,1-glucoside bond (Elbein et al., 2003), having a formula of C12H22O11 and named as α-D-glucopyranosyl α-D-glucopyranoside. Trehalose can be found in bacteria, yeast, fungi, algae, plants and invertebrates. Trehalose can contact cell membranes to maintain fluidity and thus prevent the change of membrane fusion and membrane permeability (Crowe & Crowe, 2000; Richards et al., 2002). Trehalose is not easy to be hydrolyzed by α-glucosidase, has great stability in solution, and has the solubility and osmolality similar to maltose. At 92% humidity, trehalose has 9.54% of water, and has chemical stability (Birch et al., 1963; Richards et al., 2002).
In organisms, trehalose can store energy, and protect proteins and cell membranes under heat, frozen, dry or high osmotic pressure (Newman et al., 1993). In many kinds of bacteria, trehalose can stabilize functions of cell walls (Richards et al., 2002). Trehalose can store energy in plants and animals, facilitate plants to grow in dry environments, and help yeasts to get used to changes of environment such as dryness, changes of osmotic pressure, heat shock and tolerance to alcohol (Yoshida et al., 1998). Trehalose can be used in food, medicines (Higashiyama, 2002) and biotechnology (Spriess and Ivell, 2002). A proper amount of trehalose can be used for increasing cell viability (Eroglu et al., 2000). Trehalose is proved as a GRAS (generally regarded as safe) food by FDA, and is widely used in food, cosmetics and medical products. Trehalose is used as a stabilizing agent for enzymes, proteins, biomass preparation of pharmaceutical compositions and organ transplants, used as an anti-freezing agent for vaccines and mammalian cells, and used as a moisturizing agent with liposomes (Schiraldi et al., 2002). Further, trehalose may be formed in organisms via genetic recombination.
Mannose plays critical roles in various cellular activities. Mannose is critical in activating macrophages and thus activates anti-inflammation and tissue regeneration. Macrophages have four different receptors for mannose to clean residual bodies resulting from inflammation. Mannose has anti-inflammation ability for activating fibroblasts to produce collagen and proteoglycans at healing of wounds. Mannose is considered to be natural anti-inflammation material to modulate over-activated neutrophils. All cells contain mannose, and thus mannose can affect all organs and tissues in a body. It is found that there is mannose on the photoreceptor in the retina, and plays a critical role in vision. The supplement of mannose can be combined with other treatments for diabetes patients with cataract. Mannose can maintain the metabolism of cell membranes and thus can protect eye lens.
Xerophthalmia is a medical condition in which the eye fails to produce tears due to the dryness of epithermal cells of cornea. Currently, there are various compositions such as artificial tears for treating xerophthalmia. Trehalose has great moisture retention property, and has been used in eye drops for treating xerophthalmia (Matsuo et al., 2002). JP 2003-128588 issued on May 8, 2003 discloses that the polysaccharide composition is used as a matrix in eye drops, wherein the agar can be used as a matrix of eye drops for enhancing the medicine to move into eyes. JP 2001-247466 issued on Sep. 11, 2011 discloses that an eye drop for contact lens to absorb polyvinylpyrrolidone so as to stabilize the tear film. The conventional eye drop includes polysaccharides but lacks long term moisture retention. Furthermore, small molecular weight polysaccharides in the conventional eye drop fail to activate the immune system.
Accordingly, there is a need to develop a new material for eye drops.